In heat exchangers, particularly of the type used to heat or cool fluids, it is common to use heat transfer surfaces, such as fins, positioned between, adjacent to and/or inside fluid flow passages in the heat exchanger to increase heat transfer performance. Various types of heat transfer surfaces or fins are known. One common type of heat transfer surface or fin is a corrugated fin consisting of sinusoidal or rectangular corrugations extending in rows along the length or width of the heat exchanger plates or tubes, the heat transfer surface being positioned between or adjacent to the heat exchanger tubes or stacked plates that make up the heat exchanger. In order to further increase the heat transfer performance of the heat transfer surface or fin, it is known in the art to form a series of “slits” or “louvers” in the planar surfaces of the heat transfer surfaces or fins. The slits or louvers serve to disrupt boundary layer growth along the length of the planar surfaces and increase mixing in the fluid flowing over/through the heat transfer surface in an effort to increase overall heat transfer performance of the heat exchanger.
While positioning a heat transfer surface or fin between the tubular members or stacked plates of the heat exchanger increases heat transfer performance by providing additional surface area for heat transfer, heat transfer surfaces are also known to increase pressure drop through the fluid channel in which the heat transfer surface is located. Therefore while louvered fins and other heat transfer surfaces with heat transfer augmenting features are known, there is a continual need to provide improved heat transfer surfaces that increase heat transfer performance without negatively impacting pressure drop across the fin or heat transfer surface whether it is positioned between the tubular members or within the tubular members of a heat exchanger.